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Wait, the Anubis people _didn't know_ 3 core machines were sold for years? AMD was famous for it!
by DiabloD3 1y ago
Wait, the Anubis people _didn't know_ 3 core machines were sold for years? AMD was famous for it!
- Sesse__ 1y agoWhat about... single-core machines?
- nerdsniper 1y agoSMT generally caused single-core CPU's to appear as 2 logical cores. I realize Anubis was probably never tested on a true single-core machine. They are actually somewhat difficult to find these days outside of microcontrollers.
- crote 1y agoEven in microcontrollers it is starting to become increasingly rare! We've progressed to a point where sub-$1 hobbyist chips like the RP2040 are multicore these days.
- john-h-k 1y agoThe line of code in the article is `Math.max(nproc / 2, 1)`. So 1 core yields 1 thread. Only CPUs with an odd number of cores, no SMT, and >1 core will hit this bug. Not very common
- jsheard 1y agoIn theory a CPU with SMT could still trigger this bug, because not every core necessarily has to have SMT. Intel made some chips that combined performance cores with SMT and efficiency cores without SMT, so if they had an odd number of E-cores they'd have ended up with an odd number of threads regardless.
- jeffbee 1y agoYou can also just boot linux with maxcpus=5 or any other number. Believing things about the parity of the number of CPUs is just nuts.
- deleted 1y ago[deleted]
- nerdsniper 1y agoIn their testing, even with odd numbers of physical cores, SMT caused an even number of logical cores. Some phones didn't have SMT, and also had an odd number of physical cores, but this was genuinely rare. Also, they still might not (but probably learned). In this article they imply that each type of CPU core (what they call a "tier" in the article) will still be a power of two, and one just happened to be 2^0. I'm not sure they were around when the AMD Athlon II X3 was hot. >>> Today I learned this was possible. This was a total "today I learned" moment. I didn't actually think that hardware vendors shipped processors with an odd number of cores, however if you look at the core geometry of the Pixel 8 Pro, it has three tiers of processor cores. I guess every assumption that developers have about CPU design is probably wrong.
- jeffbee 1y ago> each type of CPU core (what they call a "tier" in the article) will still be a power of two Yeah that's obviously not true, and believing it shows a marked lack of experience in the field. Of the current Xeon workstation lineup, only 3 of 14 SKUs have power-of-2 core counts. And there are consumer lines of CPUs with 6 cores and that sort of thing.
- PaulDavisThe1st 1y agoI believe that the assumption was multiple of two, not power of two.
- nerdsniper 1y agoYeah I both terribly mistyped and misrepresented Anubis' assumption. I'm sorry for that error.
- astrange 1y agoThe current Apple TV has 5 cores. No web browser though.
- masklinn 1y ago